The state of affairs of neurologic monitoring by near-infrared spectroscopy in pediatric cardiac critical care

Advanced Neuromonitoring Modalities on the Horizon: Detection and Management of Acute Brain Injury in Children

Timely detection and monitoring of acute brain injury in children is essential to mitigate causes of injury and prevent secondary insults. Increasing survival in critically ill children has emphasized the importance of neuroprotective management strategies for long-term quality of life. In emergent and critical care settings, traditional neuroimaging modalities, such as computed tomography and magnetic resonance imaging (MRI), remain frontline diagnostic techniques to detect acute brain injury. Although detection of structural and anatomical abnormalities remains crucial, advanced MRI sequences assessing functional alterations in cerebral physiology provide unique diagnostic utility. Head ultrasound has emerged as a portable neuroimaging modality for point-of-care diagnosis via assessments of anatomical and perfusion abnormalities. Application of electroencephalography and near-infrared spectroscopy provides the opportunity for real-time detection and goal-directed management of neurological abnormalities at the bedside. In this review, we describe recent technological advancements in these neurodiagnostic modalities and elaborate on their current and potential utility in the detection and management of acute brain injury.

Postoperative Cerebral Oxygen Saturation in Children After Congenital Cardiac Surgery and Long-Term Total Intelligence Quotient: A Prospective Observational Study

OBJECTIVES

During the early postoperative period, children with congenital heart disease can suffer from inadequate cerebral perfusion, with possible long-term neurocognitive consequences. Cerebral tissue oxygen saturation can be monitored noninvasively with near-infrared spectroscopy. In this prospective study, we hypothesized that reduced cerebral tissue oxygen saturation and increased intensity and duration of desaturation (defined as cerebral tissue oxygen saturation < 65%) during the early postoperative period, independently increase the probability of reduced total intelligence quotient, 2 years after admission to a PICU.

DESIGN

Single-center, prospective study, performed between 2012 and 2015.

SETTING

The PICU of the University Hospitals Leuven, Belgium.

PATIENTS

The study included pediatric patients after surgery for congenital heart disease admitted to the PICU.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Postoperative cerebral perfusion was characterized with the mean cerebral tissue oxygen saturation and dose of desaturation of the first 12 and 24 hours of cerebral tissue oxygen saturation monitoring. The independent association of postoperative mean cerebral tissue oxygen saturation and dose of desaturation with total intelligence quotient at 2-year follow-up was evaluated with a Bayesian linear regression model adjusted for known confounders. According to a noninformative prior, reduced mean cerebral tissue oxygen saturation during the first 12 hours of monitoring results in a loss of intelligence quotient points at 2 years, with a 90% probability (posterior β estimates [80% credible interval], 0.23 [0.04-0.41]). Similarly, increased dose of cerebral tissue oxygen saturation desaturation would result in a loss of intelligence quotient points at 2 years with a 90% probability (posterior β estimates [80% credible interval], -0.009 [-0.016 to -0.001]).

CONCLUSIONS

Increased dose of cerebral tissue oxygen saturation desaturation and reduced mean cerebral tissue oxygen saturation during the early postoperative period independently increase the probability of having a lower total intelligence quotient, 2 years after PICU admission.

Non-invasive optical neuromonitoring of the temperature-dependence of cerebral oxygen metabolism during deep hypothermic cardiopulmonary bypass in neonatal swine

Management of deep hypothermic (DH) cardiopulmonary bypass (CPB), a critical neuroprotective strategy, currently relies on non-invasive temperature to guide cerebral metabolic suppression during complex cardiac surgery in neonates. Considerable inter-subject variability in temperature response and residual metabolism may contribute to the persisting risk for postoperative neurological injury. To characterize and mitigate this variability, we assess the sufficiency of conventional nasopharyngeal temperature (NPT) guidance, and in the process, validate combined non-invasive frequency-domain diffuse optical spectroscopy (FD-DOS) and diffuse correlation spectroscopy (DCS) for direct measurement of cerebral metabolic rate of oxygen (CMRO₂). During CPB, n = 8 neonatal swine underwent cooling from normothermia to 18℃, sustained DH perfusion for 40 min, and then rewarming to simulate cardiac surgery. Continuous non-invasive and invasive measurements of intracranial temperature (ICT) and CMRO₂ were acquired. Significant hysteresis (p < 0.001) between cooling and rewarming periods in the NPT versus ICT and NPT versus CMRO₂ relationships were found. Resolution of this hysteresis in the ICT versus CMRO₂ relationship identified a crucial insufficiency of conventional NPT guidance. Non-invasive CMRO₂ temperature coefficients with respect to NPT (Q₁₀ = 2.0) and ICT (Q₁₀ = 2.5) are consistent with previous reports and provide further validation of FD-DOS/DCS CMRO₂ monitoring during DH CPB to optimize management.

Monitoring and management of brain hemodynamics and oxygenation

While cardiorespiratory monitoring is standard for newborns in the NICU, monitoring of brain hemodynamics and oxygenation is usually sporadic and targeted to newborns with suspected or confirmed neurologic disorders. This is unfortunate, since critically ill newborns, both preterm and term-born, are at high risk of brain injury and would benefit from improved techniques for continuous monitoring of brain hemodynamics and oxygenation, in addition to monitoring of systemic hemodynamics and oxygenation. Near-infrared spectroscopy (NIRS) and, to a lesser extent, Doppler ultrasound are techniques that have been used in research and increasingly for clinical purposes to measure and monitor brain hemodynamics and oxygenation in newborns. NIRS monitoring can be useful for detection of diverse pathologic conditions that occur frequently in very preterm newborns and in selected populations of term newborns at risk for brain injury related to disturbances of systemic hemodynamics. This chapter reviews the current state of the art with regard to brain-monitoring techniques and the research directed at this important area, and it concludes with suggestions for the use of currently available tools to manage newborns at high risk of neurologic injury from disturbances in brain hemodynamics and oxygenation.

Non-invasive assessment of cerebral oxygen metabolism following surgery of congenital heart disease

OBJECTIVES

Cerebral protection is a major issue in the treatment of infants with complex congenital heart disease. We tested a new device combining tissue spectrometry and laser Doppler flowmetry for non-invasive determination of cerebral oxygen metabolism following cardiac surgery in infants.

METHODS

We prospectively measured regional cerebral oxygen saturation cSO 2 and microperfusion (rcFlow) in 43 infants 12-24 h following corrective ( n  = 30) or palliative surgery ( n  = 13) of congenital heart defects. For comparison, cerebral blood flow (CBF) was determined by colour duplex sonography of the extracranial cerebral arteries. Cerebral fractional tissue oxygen extraction, approximated cerebral metabolic rate of oxygen (aCMRO 2 ) and cerebral metabolic rate of oxygen (CMRO 2 ) were calculated.

RESULTS

cSO 2 was lower [54.6% (35.7-64.0) vs 59.7% (44.5-81.7); P  < 0.01] after neonatal palliation, while rcFlow [69.7 AU (42.5-165.3) vs 77.0 AU (41.2-168.1); P  = 0.06] and cerebral fractional tissue oxygen extraction [0.34 (0.24-0.82) vs 0.38 (0.17-0.55); P  = 0.63] showed a trend towards lower values. We found a positive correlation between aCMRO 2 and CMRO 2 ( r  = 0.27; P  = 0.03). aCMRO 2 was significantly lower after neonatal palliation [4.0 AU (2.1-6.3) vs 4.9 AU (2.2-15.6); P  = 0.02].

CONCLUSIONS

According to our experience, combined photospectrometry and laser Doppler flowmetry enable non-invasive assessment of cerebral oxygen metabolism. The method promises new insights into perioperative cerebral perfusion following palliation or corrective surgery in infancy.

Neuroprotection of hyperbaric oxygen therapy in sub-acute traumatic brain injury: not by immediately improving cerebral oxygen saturation and oxygen partial pressure

Although hyperbaric oxygen (HBO) therapy can promote the recovery of neural function in patients who have suffered traumatic brain injury (TBI), the underlying mechanism is unclear. We hypothesized that hyperbaric oxygen treatment plays a neuroprotective role in TBI by increasing regional transcranial oxygen saturation (rSO₂) and oxygen partial pressure (PaO₂). To test this idea, we compared two groups: a control group with 20 healthy people and a treatment group with 40 TBI patients. The 40 patients were given 100% oxygen of HBO for 90 minutes. Changes in rSO₂ were measured. The controls were also examined for rSO₂ and PaO₂, but received no treatment. rSO₂ levels in the patients did not differ significantly after treatment, but levels before and after treatment were significantly lower than those in the control group. PaO₂ levels were significantly decreased after the 30-minute HBO treatment. Our findings suggest that there is a disorder of oxygen metabolism in patients with sub-acute TBI. HBO does not immediately affect cerebral oxygen metabolism, and the underlying mechanism still needs to be studied in depth.

Combined Cerebral and Renal Near-Infrared Spectroscopy After Congenital Heart Surgery

The maintenance of an adequate oxygen supply to tissues after congenital heart surgery is essential for good outcomes. The objective of this study was to assess the usefulness of near-infrared spectroscopy (NIRS) for estimating central venous oxygen saturation (ScvO2) using both cerebral and renal measurements, explore its relation with cardiac output measurements and check its ability to detect low cardiac output. A prospective observational pilot study was conducted in patients weighing <10 kg undergoing cardiopulmonary bypass surgery. Spectroscopy probes were placed on the forehead and renal area, and serial cardiac output measurements were obtained by femoral transpulmonary thermodilution over the first 24 h after surgery. In the 15 patients studied, ScvO2 was correlated with cerebral (r = 0.58), renal (r = 0.60) and combined (r = 0.71) measurements. Likewise, the systolic index was correlated with the NIRS signals: cerebral (r = 0.60), renal (r = 0.50) and combined (r = 0.66). Statistically significant differences were found in the NIRS measures registered in the 29 low cardiac output events detected by thermodilution: cerebral: 62 % (59-65) versus 69 % (63-76); renal: 83 % (70-89) versus 89 % (83-95); and combined 64 % (60-69) versus 72 % (67-76). In our series, combined cerebral and renal monitoring was correlated with central venous oxygen saturation and cardiac output; low cardiac output detection associated a different spectroscopy pattern.

Intraoperative changes in blood pressure associated with cerebral desaturation in infants

BACKGROUND

Intraoperative hypotension has been linked to poor postoperative neurological outcomes. However, the definition of hypotension remains controversial in children. We sought to determine arterial blood pressure threshold values associated with cerebral desaturation in infants.

METHODS

After ethics committee approval, infants younger than 3 months were included in this prospective observational study. Cerebral saturation was assessed using near-infrared spectroscopy. The primary goal of the study was to determine percentage reductions in intraoperative systolic blood pressure (SBP) and mean blood pressure (MBP) associated with decreases in cerebral blood oxygen saturation of >20%, when compared to baseline. Analyses were performed using a bootstrap receiving operator characteristic (ROC) curves with determination of the gray zone.

RESULTS

Sixty patients were recruited and 960 measurement points were recorded. Fifty-nine data points (6.1%) recorded cerebral desaturation of >20% when compared to baseline. The areas under the ROC curves were 0.79 (0.74-0.84) and 0.67 (0.6-0.75) for percentage decreases in SBP and MBP, respectively. Gray zone values with false-positive and negative rates <10% were SBP decreases of 20.5% and 37.5%, respectively, and MBP decreases of 15.5% and 44.5%, respectively.

CONCLUSION

Our results indicate that falls in noninvasive systolic blood pressure of <20% from baseline are associated with a <10% chance of cerebral desaturation in neonates and infants <3 months of age undergoing noncardiac surgery. As such, maintaining systolic blood pressure above this threshold value appears a valid clinical target.